A problem in utilization of time division multiple access (TDMA) space satellite communication facilities has been to strike an advantageous balance between station costs and network performance; one factor of the latter being the proportionate "throughput" of information bits to non-information bits (e.g. bits used for time control, error control, etc.).
Another problem has been to provide modular time division multiplex (TDM) switching centers for such facilities, which can be conveniently assembled into various station (access node) configurations without precise foreknowledge of station traffic and geographic coverage.
Another problem has been to provide for efficient acquisition, timekeeping and use of satellite time in such networks.
Another problem has been to provide multiple routing capability in modular units relative to a TDMA facility.
Another problem has been to provide efficient terrestrial linkage of a large geographic area to one station (access node) of a TDMA space satellite facility.
Another problem has been to provide for efficient multiplex switching and high speed transmission of diverse digital signal traffic -- including telephone (encoded voice), data and non-coded image (NCI) information -- by satellite and over point-to-point terrestrial links between physically remote switching centers of one station.
An object of the present invention is to provide a method of communication fulfilling requirements associated with eliminating the foregoing problems and satisfying respective needs.
Another object is to provide an architecture for modular time domain switching centers, and a related method of communication, which fulfill the foregoing requirements.
Other objects are to provide modular "store and forward" digital switching centers, for operating hierarchically in stations covering a variety of "use-interface" areas relative to access nodes of a TDMA principal trunk facility, and a method of operating a network of such stations.
Another object is to provide a method of TDMA satellite communication characterized by use of modular unit terminals (representing small increments of equipment and cost), to provide call switching, time compression, activity compression and distributed demand assignment and thereby provide a basis for achieving station and network efficiencies relative to use of the satellite.
Another object is to provide a method of efficiently switching and handling data and encoded sound (telephone) signals relative to a TDMA link.
A feature of the invention is the use of modular hierarchical switching and activity compressing units in access stations interfacing with a TDMA link, with units linked intranodally (within a station region) by subsidiary digital trunks and with stations linked nodally by a principal TDMA trunk; nodally associated centers operating to provide hierarchical multiplexing, compression and switching of digital signal traffic relative to associated access nodes of the TDMA link.
Another feature of the invention is the use of said units in reverse hierarchical order to provide progressive decompression and demultiplexing of composite signals received from the TDMA link.
Another feature is the use of plural digital trunks (such as leased high speed public carrier lines), as TDM links between hierarchically associated switching centers associated with a station having access to a space satellite facility. A related feature is the use of individual lowest level centers in the station hierarchy to control establishment and release of local and toll (satellite) call connections and the use of highest level centers to control acquisition, timekeeping and demand assignment relative to the satellite.
Another feature is the use of land-linked multiplex switch modules to administer time and space domain connections to time division transmission facilities having fixed time capacity to handle a wide range of mixed voice and data traffic in block multiplex relative to a satellite; the extra cost of storage for block handling (over bit handling) being offset by reductions in transmission overhead relative to the land links and the satellite.
Another feature is the terrestrial connection of plural first level switching modules with an access node of a TDMA space segment through land-based digital trunks and a common second level switching module; said first and second level modules operating hierarchically to switch, buffer and activity compress traffic signals passing between multiple independent source/reception ports and the satellite.
Another feature is the linked association of a first level TDM switching center with plural second level TDM switching centers which in turn link to different access nodes (stations) of a TDMA facility. A related feature is the association of plural co-located second level TDM switching centers with one or more access nodes of a TDMA facility. A variation is the association of plural co-located second level TDM switching centers with different TDMA carrier frequency bands (transponders) of a satellite repeater and common timekeeping apparatus.
Another feature is the provision of a basic module structure which can be adapted for first level switch operation, second level operation or both (for co-location of station elements).